BMI is a weight-to-height ratio. It is determined by dividing a person's weight by the square of their height. People with a BMI above 30.0 are considered obese. Waist-to-hip ratio is determined by dividing waist circumference by hip circumference. People with bigger bellies compared to their hips have higher ratios. Men above 0.90 and women above 0.85 are considered to be centrally obese.

"Existing research has linked brain shrinkage to memory decline and a higher risk of dementia, but research on whether extra body fat is protective or detrimental to brain size has been inconclusive," said study author Mark Hamer, PhD, of Loughborough University in Leicestershire, England. "Our research looked at a large group of people and found obesity, specifically around the middle, may be linked with brain shrinkage."

Study - People - Age - Group - Percent

The study looked at 9,652 people with an average age of 55. Of that group, 19 percent were determined to be obese. Researchers measured BMI, waist-to-hip ratio and overall body fat and surveyed participants about their health. Researchers then used magnetic resonance imaging to determine brain volumes for white and gray brain matter and volumes in the various regions of the brain.

Gray matter contains most of the brain's nerve cells and includes brain regions involved in self-control, muscle control and sensory perception. White matter contains nerve fiber bundles that connect various regions of the brain.

Factors - Brain - Volume - Age - Activity

After adjusting for other factors that may affect brain volume, such as age, physical activity, smoking and high...